Question: Solve for $x$ and $y$ using substitution. ${3x+6y = 3}$ ${x = -4y-5}$
Explanation: Since $x$ has already been solved for, substitute $-4y-5$ for $x$ in the first equation. ${3}{(-4y-5)}{+ 6y = 3}$ Simplify and solve for $y$ $-12y-15 + 6y = 3$ $-6y-15 = 3$ $-6y-15{+15} = 3{+15}$ $-6y = 18$ $\dfrac{-6y}{{-6}} = \dfrac{18}{{-6}}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = -4y-5}\thinspace$ to find $x$ ${x = -4}{(-3)}{ - 5}$ $x = 12 - 5$ ${x = 7}$ You can also plug ${y = -3}$ into $\thinspace {3x+6y = 3}\thinspace$ and get the same answer for $x$ : ${3x + 6}{(-3)}{= 3}$ ${x = 7}$